As a liquid fluid used in various industries, there are a variety of liquid fluids beginning with, for example, liquid sodium for coolant for fast breeder reactor, a heat medium for heat exchanger that is arranged in various facilities, and an incompressible fluid for hydraulic machine. These liquid fluids have several properties specific to their materials. When judged from purpose of use, some properties are desired to be enhanced further, and some properties are desired to be suppressed further. For example, the liquid sodium for cooling has such an intense reactivity that an explosion occurs when it comes in contact with air or water.
Relation between a property specific to such a liquid fluid and a property desired in view of a purpose of use is further discussed below with an example of liquid sodium for cooling.
The reasons that sodium is used as a coolant for fast breeder reactor exist in excellent properties that liquid sodium has, for example; (i) a thermal conductivity of sodium is about 100 folds that of water, and sodium is capable of conducting heat effectively; (ii) sodium hardly moderates neutron and has good compatibility with nuclear reactor materials; (iii) sodium has a boiling point as high as about 880° C., and therefore, when thermal energy is converted into steam at a heat transfer end, it is possible to obtain steam with a temperature as high as about 480° C., resulting in that electric power generation with better thermal efficiency becomes possible; (iv) since the boiling point of sodium (about 880° C.) is higher than about 500° C. that is an operation temperature for fast breeder reactor, liquid sodium can be kept in liquid as it is without application of pressure and no high pressure is necessary to be applied to nuclear reactor and pipelines, and therefore, even if a sodium leak occurs, it does not blow out rapidly, and there is no fear to lose cooling capacity of the nuclear reactor (Non-patent document 1).
On the other hand, sodium has a property of such an intense reactivity that an explosion occurs when sodium comes in contact with air or water. However, in view of a purpose to utilize sodium as a coolant for fast breeder reactor, this property is a property that should be suppressed because there is a possibility that sodium comes in contact with air or water when it leaks from piping or the like.
Non-patent document 1: Kiso Kousokuro Kougaku Henshu Iinkai (edited): Kiso Kousokuro Kougaku, published by Nikkan Kogyo Shimbun, LTD (October, 1993).